The background description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.
Some semiconductor processing systems may employ plasma when depositing thin films on a substrate in a processing chamber. Generally, the substrate is arranged on a pedestal in the processing chamber. To create the thin film using chemical vapor deposition, one or more precursors are supplied by a showerhead to the processing chamber.
During processing, radio frequency (RF) power may be supplied to the showerhead or to an electrode to create plasma. For example, RF power may be supplied to the electrode embedded in a pedestal platen, which may be made of a non-conducting material such as ceramic. Another conducting portion of the pedestal may be connected to RF ground or another substantially different electrical potential.
When the electrode is excited by the RF power, RF fields are generated between the substrate and the showerhead to create plasma between the wafer and the showerhead. When the pedestal platen is made of ceramic, the RF fields will also appear under and beside the pedestal platen and give rise to parasitic plasma. Parasitic plasma may be reduced or eliminated in certain regions if the electric fields penetrating these regions can be reduced. One way to reduce or eliminate the electric fields is to use a grounded RF shield. However, if the RF shield is not designed properly, it can give rise to a low RF impedance path to ground.
One way to prevent excessive RF coupling to ground is to use a solid dielectric layer between ground and the electrode. However, the thickness of the solid dielectric layer that is required to achieve low coupling capacitance to ground is generally not practical.